The present invention relates to a choke coil utilized in electronic products both for consumer and industrial uses.
Thanks to the development of various electronic devices, electronic products have become smaller and thinner in size, consume power, and have better performance. And yet, the market""s demand for the better products still continues. In order to meet this demand, a power supply section, particularly in a switching power supply, has struggled with the following three major demands: 1. accommodating a higher switching frequency, 2. employing a higher density of parts mounting, particularly when utilizing surface mounting techniques, 3. accommodating a large current responsive to a higher performance of semiconductor, etc. Accordingly, a demand has arisen for a choke coil, one of the major parts of the switching power supply, having a smaller loss, that accommodates a larger current, and is smaller and thinner for use with surface mounting techniques.
A conventional thin-type choke coil well known in the market is illustrated in FIGS. 47 through 51. FIG. 47 is an exploded perspective view, FIG. 48 is a perspective view depicting the coil incorporated with a closing magnetic core. FIG. 49 is a perspective view depicting a complete product. FIG. 50 is a cross section, and FIG. 51 is a top view depicting the coil from which one magnetic core is removed.
The following elements are illustrated in the above Figs.: flat type wire 1 covered by an insulated material, coreless coil 2, an inner turn 3 of the coreless coil 2, an outer turn 4 of the coreless coil 2, a terminal 5 of the inner turn 3, a terminal 6 of the outer turn 4, a center magnetic leg 7, an outer magnetic leg 8, a common magnetic yoke 9, a closing magnetic core 10 of magnetic field, an insulating paper 11, a window height 12 of the closing magnetic core 10. The structure of the conventional thin-type choke coil is as follows: The coreless coil 2 is formed by coiling the flat type wire 1. The inner terminal 5 and the outer terminal 6 are coupled with an inner turn 3 and outer turn 4 of the coreless coil 2 respectively by e.g., soldering. The coreless coil 2 and the insulating paper 11 are disposed around the center magnetic leg 7 of the closing magnetic core 10.
In the above structure, however, the inner terminal 5 coupled with the inside turn 3 of the coreless coil 2 is led out from a clearance between the coreless coil 2 and the common magnetic yoke 9 of the closing magnetic core 10, thus a thickness of the inner terminal 5 is added to the window height 12 of the closing magnetic core 10, whereby a dead space is produced in the window height direction. As a result, a space factor lowers and the choke coil cannot be further slimmed.
In addition, since the inner terminal 5 is led out from the clearance between the coreless coil 2 and the common magnetic yoke 9, a sectional area of the inner terminal 5 cannot be enlarged. Thus, the choke coil cannot accommodate a larger current.
The present invention aims to provide a thinner choke coil by lowering the height, and a choke coil which can accommodate a larger current as well.
In order to address the above problems, the choke coil according to the present invention comprises the following elements:
(a) a closing magnetic core having a center magnetic leg, an outer magnetic leg and a common magnetic yoke,
(b) a coreless coil made of a coiled plate-type-wire comprising a flat-type-wire or foil-type-wire, having terminals on both ends of the plate-type-wire.
The coreless coil is disposed around the center magnetic leg of the closing magnetic core, and at least an inner terminal of the terminals is led out from a notch or an opening provided on the common magnetic yoke of the closing magnetic core. Thus the thickness of the inner terminal of the coreless coil does not influence the window height of the closing magnetic core. As a result, no dead space is allowed in the window height direction, the space factor increases, and the window height of the closing magnetic core can be lowered, whereby a thinner choke coil is realized. At the same time, the thickness as well as the cross area of the inner terminal can be increased so that the choke coil can accommodate a larger current.